This invention relates to materials handling vehicles having load-engaging clamps, and particularly to automatically-guided, driverless vehicles having clamps with automatic sensing functions.
Some load clamps having automatic sensing functions have existed in the past as evidenced, for example, by Smith U.S. Pat. No. 3,037,651 and Inaba et al, U.S. Pat. No. 4,423,998. Both of these clamps have sensors for regulating the forward approach of the load-engaging clamp pads to a cylindrical load prior to clamping so that, when the clamp arms ultimately close, the pads will engage the load in the proper position. However, both of these clamps require that the clamp pads ultimately extend forwardly of a forwardly-facing curved surface of the load (such as the rear surface of the axial opening of the roll in Smith, or the forward edge of the cylindrical load in Inaba). The problem with this type of structure is that many loads, such as ordinary cartons, require precise positioning of the clamp pads relative to a forwardly-facing load surface, but require that the pads not protrude forwardly of such surface because such protrusion would be likely to interfere with forwardly adjacent walls or other loads during engagement or depositing of the load. The Smith and Inaba structures can therefore not be used for cartons or other similar types of loads.
Moreover, load clamps for automatically-guided vehicles need to sense many other conditions involving the load itself, or the surfaces or objects surrounding the load, since the vehicle has no human operator to compensate for any variables with respect to these conditions. Such additional necessary sensing functions, not provided by the prior art, include the sensing of other forward-approach parameters such as obstacles between the clamp arms and forwardly thereof. For example, if a clamped load is to be deposited in a predetermined space, and an obstacle exists to the depositing of the load (such as the presence of another load in the space) sensors are required to detect this condition and interrupt the depositing operation. Or if the vehicle is moving forwardly without a clamped load and an object is sensed between the clamp arms and forwardly thereof in a location where no such object should exist, vehicle operation should likewise be interrupted. Also, if obstacles exist immediately ahead of the clamp arms, rather than in the forward space between them, this indicates that a load to be engaged, or an adjacent load, is transversely offset and will block full advancement of the clamp arms to a load-engaging position. In such case advancement of the clamp arms should be interrupted.
In addition to sensors governing the forward advancement of the clamp arms, sensors regulating vertical movement of the clamp arms on the vehicle'3 s load-elevating mast are likewise needed. For example, when a carton is to be engaged, it is necessary that the clamp pads be lowered to within a predetermined distance of the bottom of the carton, to ensure proper load engagement. Moreover, when a load is clamped, the presence of any sag in the bottom of the load, or any obstacle in a space where it is intended to deposit the load, should be sensed and the vertical movement of the clamp structure halted. Alternatively, when a clamped load is to be deposited at an elevated position on another load or other supporting surface, the presence or absence of such supporting surface should be sensed to determine if it is actually present before the load is released.
In addition to obstacles located forwardly and vertically with respect to the clamp arms, there is a need to sense obstacles located transversely outwardly of the clamp arms. For example, if opening of the clamp arms results in contact with such an obstacle, such opening should be interrupted. Alternatively, if forward or rearward motion of the vehicles results in such contact, such motion should likeiwse be interrupted.
Finally, conditions preventing floor-supported loads from being level, either in a transverse or forward direction, need to be sensed to avoid improper engagement of such loads.
Sensors have previously been used for aiding in the positioning of load-handling forks, as shown, for example, in Lemelson U.S. Pat. No. 3,486,640, Ohntrup et al., U.S. Pat. No. 3,672,470, Peterson et al, U.S. Pat. No. 4,212,375 and Ahlbom U.S. Pat. No. 4,279,328. However, because forks engage loads from beneath, rather than from the sides and from above, sensing principles applicable to forks are not useful in solving the problems of load clamps.